This invention relates to a set of keyed electrical connectors comprising a first and a second plug connector and a first and a second receptacle connector. The invention particularly, but not exclusively, concerns such a set of connectors which are shielded in respect of electro-magnetic induction.
U.S. Pat. No. 4,457,575, for example, discloses a keying system for shielded plug and receptacle electrical connectors, in which keys in the form of ribs and complimentary keyways therefor are provided on the dielectric housings of the connectors and are located to ensure that only an individual receptacle connector can be mated with a specific plug connector. There is disclosed in U.S. Pat. No. 3,491,330 shielded rectangular plug and receptacle connectors having corners thereof chamfered for polarizing purposes, that is to say, for ensuring that the plug and a receptacle connector can be mated only in a predetermined orientation relative to each other. The German Patent 554,477 discloses a set of unshielded plug and socket connectors having on the housings thereof, keys and corresponding keyways, in the form of ribs and grooves, for keying particular plugs to particular sockets. Some of the plugs are mateable with more than one of the sockets. There is disclosed in U.S. Pat. No. 5,017,156, a shielded plug connector and a shielded receptacle connector, the receptacle connector comprising a metal shielding shell containing an assembly of electrical terminals, the shielding shell acting as a mating portion of the receptacle connector, for receiving the shielded plug connector.
There are some applications, for example, in the computer industry, where a first circuit is required to be connectable only to a second circuit and a third circuit is required to be connectable not only to the first circuit but alternatively to a fourth circuit. For example, one of a pair of surface mount electrical receptacle connectors the terminals of each of which are connected to a respective printed circuit, may be required to be capable of receiving only one of a pair of plug connectors each connected to a different circuit, remote from the receptacle connectors, by means of a cable of a particular length, whereas the other receptacle may be required to be capable of receiving either one of the plug connectors, as needed.
An object of the present invention is to provide a set of plug and socket electrical connectors which is suitable for use in an application of the kind outlined above.